Implantable medical devices, such as neurostimulators, pacemakers, and implantable cardio defibrillators (ICD), and external systems, such as programmers and patient monitors, communicate with each other during implant and after implant for purposes of device programming and data acquisition. For example, during device implantation a physician may evaluate a patient's condition by using the implanted device to acquire real-time physiological data from the patient and communicating the physiological data in real-time to an external programmer for processing and/or display. The physician may also program the implantable device based on the patient's condition and needs. After device implant, communication between the implantable device and an external system facilitates device reprogramming, and device interrogation during which device operation data and patient physiological data acquired by and stored in the implantable device are transmitted from the device to the external system.
Implantable medical devices and external systems communicate by way of telemetry. One type of telemetry is based on inductive coupling between two closely-placed coils using the mutual inductance between these coils. This type of telemetry is referred to as inductive telemetry. It may also be referred to as near-field telemetry due to the closeness of coils. In one example of inductive telemetry, an implantable device includes a communication interface with a first coil coupled to a transceiver, and the external system includes a communication interface with a second coil coupled to a transceiver. The communication interface of the external system may be embodied in a handheld device, e.g., wand, that is electrically connected to another component of the external system, such as a programmer computer.
To establish an inductive telemetry communication link between the implantable device and the external system, the wand is positioned over the patient in the area of the implanted device to place the coil of the wand in close proximity to the coil of the implantable device. The position of the wand relative to the implantable device affects the quality of the inductive communication link between the implantable device and the external system. For example, while a good quality inductive communication link between the device and system may exist initially, because the wand is handheld, it may move during a communication session to a position relative to the implantable device that reduces the quality of the inductive communication link or breaks the inductive communication link entirely. In some cases, communication errors may occur even if the external communication interface is not moved. For example, if the noise level, e.g., electrical signal interference, within the area of the communication session increases, communication errors may occur. Environmental conditions, such as the presence of metal near the devices, may also affect the communications link.
Another type of telemetry is radio frequency (RF) telemetry, which involves the transmission and reception of RF signals through antennas. In one example of RF telemetry, an implantable device includes a communication interface with a first antenna coupled to a transceiver, and the external system includes a communication interface with a second antenna coupled to a transceiver. This type of telemetry may also be referred to as near-field telemetry in cases where the implantable device and the external system are within close range of each other.
To establish a RF telemetry communication link between the implantable device and the external system, the patient with the implantable device is positioned in the area of the external system, e.g., within the same room. The positions of the implantable device and the external system relative to each other may affect the quality of the RF communication link between the implantable device and the external system. For example, while a good quality RF communication link between the device and system may exist initially, the patient with the implantable device may move during a communication session to a position relative to the external system that reduces the quality of the RF communication link or breaks the RF communication link entirely. In some cases, communication errors may occur even if the patient does not move. For example, if the noise level, e.g., electrical signal interference, within the area of the communication session increases, communication errors may occur. Environmental conditions, such as the presence of metal near the devices, may also affect the communications link.
There is a need in the implantable medical device field for communication apparatuses and methods that maintain quality communication between an implantable device and external device in the face of changing operational conditions including for example, a change in relative positions between the implantable device and the external system, or a change in the environment within which communication is taking place. The apparatuses and methods described below fulfil these needs.